DESCRIPTION (from the application): More and more people in this country live at least part of their lives alone. Teenagers grow up with parents off at work, and often substitute computers or the Internet for the companionship of peers. Increasing divorce rates bring isolation to many in the middle years, and the death of a spouse is an expected fact of later life. The result is social isolation and, presumably, loneliness for many. Epidemiological and prospective studies have identified social isolation as a major risk factor for psychological disturbances and for broad-based morbidity and mortality. Most studies have focused on the amount of those in the social network rather than the emotional experience of loneliness resulting from personal relationships. Accordingly, the behavioral, psychological, and biological mechanisms responsible for the epidemiological relationship between social isolation and health are not well understood. We seek to examine four specific social-psychophysiological pathways in a 5-year longitudinal study of a representative Community sample of 230 older adults, 50-64 years of age. Aim 1 of Project 1 is to determine predictors of loneliness cross-sectionally in Year 1 and to examine the temporal stability of loneliness in older adults over a 5-year period. Aim 2 is to follow-up our prior research linking loneliness to relatively high total peripheral resistance and blood pressure and disrupted sleep; and to examine whether loneliness is related to elevated hypothalamic pituitary adrenocortical (HPA) activation and poorer health behaviors. The specificity of these associations will be determined by statistically controlling for correlated variables (e.g., hostility, depression, attachment style, anxiety). Finally, as recent reviews of the literature have noted, "it is not clear whether the differences that have been found between lonely people and those not lonely reflect differences in their behavior or in their perceptions" (Berscheid & Reis, 1998, p. 244). Aim 3, therefore, is to examine whether lonely and nonlonely individuals differ in their exposure to stressors (differential exposure) or their reactivity to stressors (differential reactivity), and/or their recovery from stressors (differential recovery).